not really qualified to talk about it but calling more in position and schooling people postflop can work well. Amazing how bad ppl are at playing postflop, wheras most good/average players play close to optimal pre.
with 20BB stacks?
In scenario one, you should be reshoving - not reraising. And if you reraise, it should be in order to snapcall someone really spewy who you have trapped.
As for scenario four, at the late stages of tournaments, you need to be stealing blinds or restealing over raises an awful lot.
Get aggressive - don't worry so much about busting. You should be busting more often in huge pots - and the times you win them be in great shape to destroy a tournament deep into the money.